<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="../css/reset.css">
    <style>
        .shadow {
            width: 200px;
            height: 200px;
            background-color: rgba(0, 0, 0, 0.5);
            position: absolute;
            left: 100px;
            top: 100px;
        }
    </style>
</head>

<body>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
</body>
<script>

    // 问题1:  posX  posY 变量跨作用域 => 提取到两个作用域都能访问的位置(dragEle)
    // 问题2: 如何将posX posY存储到dragEle?


    function dragEle(ele) {
        var obj = {
            target: ele,
            dragStart: function () { // dragEle.dragStart();
                // this -> dragEle对象

                // 多个函数嵌套  this指向混乱的问题
                // 1. 提前声明中间变量记录this的指向   _this = this; that = this;
                // 2. 借助箭头函数

                var _this = this; // _this = dragEle    提前声明中间变量记录this的指向  

                // 拖拽开始 在目标元素上按下 记录按下的位置 
                this.target.onmousedown = function (e) {
                    // this-> 指向绑定事件的元素 shadow

                    var e = e || window.event;
                    var posX = e.offsetX;
                    var posY = e.offsetY;
                    console.log(posX, posY);
                    _this.posX = posX;
                    _this.posY = posY;
                    console.log(_this);  // 自己没有找父作用域 =>  dragEle 

                    // 先按下 => 按下时绑定移动和松开事件
                    _this.dragMove();
                    _this.dragEnd();
                }
            },
            dragMove: function () { //  dragEle.dragMove();
                // 鼠标在文档中移动时,元素跟随鼠标移动
                // this -> dragEle对象 

                document.onmousemove = () => {
                    // 箭头函数  => this(依赖于父作用域的this执行 this->dragEle)
                    var e = e || window.event;
                    var x = e.pageX - this.posX;
                    var y = e.pageY - this.posY;
                    console.log(x, y);

                    this.target.style.left = x + "px";
                    this.target.style.top = y + "px";

                }
            },
            dragEnd: function () {
                // 鼠标在文档中任意位置松开时  清除移动
                document.onmouseup = function () {
                    document.onmousemove = null;
                    document.onmouseup = null;
                }

            }
        }
        obj.dragStart();
        return obj;
    }

    var shadowList = document.querySelectorAll(".shadow");

    for (var i = 0; i < shadowList.length; i++) {
        var shadow = shadowList[i];
        var o = dragEle(shadow);
        console.log(o);
    }









</script>

</html>